Medical viewing system and method for enhancing structures in noisy images

ABSTRACT

A viewing system and method for enhancing objects of interest represented on a moving background in a sequence of noisy images and for displaying the sequence of enhanced images, comprising extracting means ( 11 ) for extracting features related to an object of interest in images of the sequence; registering means ( 12 ) for registering the features related to the object of interest with respect to the image referential, yielding registered images ( 13 ); similarity detection means for determining the resemblance of the representations of a registered object of interest in succeeding images and weighing means for modulating the intensities of the pixels of said object of interest over the images of the sequence; temporal integrating means ( 14, 33   b ) for integrating the object of interest and the background over a number, or at least two, registered images ( 13 ) of the sequence; and display means ( 54 ) for displaying the processed images ( 15, 45 ) of the enhanced registered object of interest on faded background. Application: Medical Imaging. X-ray Fluoroscopic Imaging.

The invention relates to a viewing system for enhancing objects ofinterest represented in a sequence of noisy images including temporalenhancement and for displaying the sequence of enhanced images. Theinvention also relates to a computer executable image processing methodto be used in said system and to a medical examination apparatus coupledto such a system. The invention finds for example its application in themedical field of cardiology, for enhancing thin objects of interest suchas stents and vessel walls in angiograms.

A method for improving the visualization of low-contrast structures inmedical images is already known from the publication entitled “Layerdecomposition of coronary angiograms”, by Robert A. Close et al, inProceedings of the SPIE International Society for Optical Engineering,Vol. 3979, pages 1230-1234, 2000. This document describes an imageprocessing method for improving the detection of low-contrast featuressuch as stents in coronary x-ray images or angiograms. The basis forlayer decomposition of coronary angiograms is the observation thatalthough the anatomical motion is inherently three-dimensional andnon-uniform, the motion of a small region can usually be approximated bya single rigid motion. In projection images, all layers contribute tothe intensity of each pixel. Therefore, by decomposing an angiographicimage sequence into moving layers, it is expected to separate thedensitometric profile of the vessel from background structures that havedifferent motion. Layer decomposition models the projections as a set ofsuperposed layers moving with translation, rotation, and scaling. Thelayer motions are solved by using phase correlation techniques. Thelayer densities are solved by averaging along moving trajectories andsubtracting new layer densities from previous layer estimates. Thereconstructed vessel layer represents a motion-compensated temporalaverage of structures co-moving with the vessel. Subtraction ofbackground layers from the original image sequence yields a trackedbackground-subtracted sequence that has no vessel-motion artifacts andalmost no increase in noise, unlike standard background subtractiontechniques. This method deeply relies on a localized block-matching(phase correlation) technique applied to every layer. This techniqueestimates separately the motion of the vessels and the motion of thebackground in order to subtract the motion of the background from theoriginal image. Due to layer decomposition and block-matching, thismethod would present a calculation load actually too heavy for real timeprocessing of an image sequence during an intervention phase. So, theproposed method may be preferably used in a post-intervention phase.

Instead, it is an object of the invention to propose a viewing systemthat has means to process images in real time. It is particularly anobject of the invention to propose a medical viewing system that hasmeans to process medical images in real time in order to be dynamicallydisplayed during an intervention phase. The invention has especially foran object to provide means for enhancing low-contrast objects ofinterest, for minimizing noise and for fading the background in noisyimages such as a sequence of medical fluoroscopic images. The inventionhas particularly for an object to provide means to process angiogramsrepresenting vessels and stents as objects of interest, which present alow contrast, which may be moving on the background, but notnecessarily, and which have previously been detected and localized.

A stent is a surgical stainless steel coil that is placed in the arteryin order to improve blood circulation in regions where a stenosis hasappeared. When a narrowing called stenosis is identified in a coronaryartery of a patient, a procedure called angioplasty may be prescribed toimprove blood flow to the heart muscle by opening the blockage. Inrecent years, angioplasty increasingly employs a stent implantationtechnique. This stent implantation technique includes an operation ofstent placement at the location of the detected stenosis in order toefficiently hold open the diseased vessel. The stent is wrapped tightlyaround a balloon attached to a monorail introduced by way of a catheterand a guide-wire. Once in place, the balloon is inflated in order toexpand the coil. Once expanded, the stent, which can be considered as apermanent implant, acts like a scaffold keeping the artery wall open.The artery, the balloon, the stent, the monorail and the thin guide-wireare observed in noisy fluoroscopic images. These objects show lowradiographic contrast that makes evaluation of the placement andexpansion of said stents at an accurate location very difficult. Also,during the operation of stent implantation, the monorail, with theballoon and stent wrapped around it, is moving with respect to theartery, the artery is moving under the influence of the cardiac pulses,and said artery is seen on a background that is moving under theinfluence of the patient's breathing. These movements make the followingof stent implantation under fluoroscopic imaging still more difficult tovisualize. In particular, these movements make zooming inefficientbecause the object of interest may get out of the zoomed image frame.Clinical problems are associated with inadequate expansion of the stent,improper placement of the stent, and gap or overlap between severalstents. Inadequately deployed stents can cause thrombosis. An otherdrawback of the bad images that were until now to the disposal of theclinician, is that it was necessary to use a contrast agent in a productintroduced in the balloon for inflating said balloon in the operation ofstent deployment. The use of the contrast agent prevents the clinicianto distinguish the stent from the balloon and from the wall of theartery.

According to the invention, a viewing system and an image processingmethod are provided comprising means for acquiring a sequence of images,and for processing and displaying said images in real time. The systemcomprises initialization means applied to the original images forextracting and localizing an object of interest, which may be movingwith respect to the referential of the image, the background beingmoving both with respect to said referential and with respect to theobject. The initialization means then comprise registration means forregistering the object of interest with respect to the referential ofthe image. According to the invention, this system further comprisesprocessing means for automatically enhancing the object of interest, forminimizing the noise and for blurring or fading the background of theimages. Said processing means include at least a means for carrying outa temporal integration technique performed on at least two images wherethe object of interest has been registered with respect to thereferential of the images. Since after registration of the object, thebackground still moves with respect to the referential of the images,this temporal integration technique provides an enhancement of theobject of interest, while minimizing the noise and blurring and fadingthe background.

Such a system is claimed in claim 1 and detailed embodiments are claimedin dependent claims. An image processing method to be used in thesystem, a program product to implement the steps of the method of theinvention, and an examination apparatus associated to such a system arefurther claimed.

Embodiments of the invention are described hereafter in detail inreference to diagrammatic figures wherein:

FIG. 1A and FIG. 1B are functional block diagrams of the system of theinvention;

FIG. 2A to FIG. 2C illustrate intervention steps of angioplasty;

FIG. 3 illustrates a step of marker registration;

FIG. 4A shows an original angiogram and FIG. 4B shows a processed imagewith zooming on an enhanced object of interest and with backgroundfading;

FIG. 5 is a functional block diagram of a medical examination apparatus.

The invention relates to a viewing system, and to a computer executableimage processing method that is used in the viewing system, forenhancing objects of interest in a sequence of noisy images and fordisplaying the sequence of enhanced images. The viewing system andmethod have means to acquire, process and display the images in realtime. The viewing system and the image processing method of theinvention are described hereafter as a matter of example in anapplication to the medical field of cardiology. In said application, theobjects of interest are organs such as arteries and tools such asballoons or stents. These objects are observed during a medicalintervention called angioplasty, in a sequence of X-ray fluoroscopicimages called angiograms. The system and method may be applied to anyother objects of interest than stents and vessels in other images thanangiograms. The objects of interest may be moving with respect to theimage referential, but not necessarily, and the background may be movingwith respect to the object or to the image referential.

The embodiments described hereafter uniquely relate to an imageprocessing system and an image processing method, and not to adiagnostic method. However, the images are acquired, in this example, asa sequence of images during a stent implantation, which is a medicalintervention performed under fluoroscopy, and which usually comprisesseveral steps for enlarging an artery at the location of a lesion calledstenosis. Fluoroscopy is a low dose x-rays technique that yields verynoisy and low contrasted images. Introducing a catheter in a patientartery in these conditions is a very delicate and dangerous operation.The embodiments of the invention do not permit the clinician to form adiagnosis. They only permit to provide the clinician, in real time, withgreatly improved medical images with respect to the fluoroscopic imagesof the same objects that the clinician would have obtained without thesystem of the invention. In a preliminary step, the practitionerlocalizes the stenosis 80 a in a patient's artery 81 as best aspossible. A corresponding medical image is schematically illustrated byFIG. 2A. Then, the sequence of images to be processed is acquired asseveral sub-sequences during the steps of the medical intervention,comprising:

a) A sub-sequence of medical images, schematically illustrated by FIG.2A, which displays the introduction in the artery 81 through a catheter69 of a thin guide-wire 65 that extends beyond the extremity of thecatheter 69, and passes through the small lumen 80 a of the artery atthe location of the stenosis; the introduction of a first monorail 60,which is guided by said guide-wire 65 having a first balloon 64 wrappedaround its extremity, without stent; and the positioning of said firstballoon 64 at the location of the stenosis 80 a using theballoon-markers 61, 62.

b) A sub-sequence of medical images, schematically illustrated by FIG.2A and FIG. 2B, which displays the inflation of this first balloon 64for expanding the narrow lumen 80 a of the artery 81 at the location ofthe stenosis to become the enlarged portion 80 b of the artery; then,the removal of the first balloon 64 with the first monorail 60.

c) A sub-sequence of medical images, schematically illustrated by FIG.2B, which displays the introduction of a second monorail 70 with asecond balloon 74 a wrapped around its extremity, again using thecatheter 69 and the thin guide-wire 65, with a stent 75 a wrapped aroundsaid second balloon 74 a; and the positioning said second balloon withthe stent at the location of the stenosis in the previously expandedlumen 80 b of the artery 81 using the balloon-markers 71, 72. In asecond way of performing the angioplasty, the clinician may skip stepsa) and b) and directly introduce a unique balloon on a unique monorail,with the stent wrapped around it.

d) A sub-sequence of medical images, schematically illustrated by FIG.2C, which displays the inflation of the second balloon 74 a to becomethe inflated balloon 74 b in order to expand the coil forming the stent75 a that becomes the expanded stent 75 b embedded in the artery wall.In the second example, the unique balloon is directly expanded both toexpand the artery and deploy the stent.

Then, considering the deployed stent 75 b as a permanent implant, thesub-sequence of medical images, displays the removing of the second (orunique) balloon 74 b, the second (or unique) monorail 70, the guide-wire65 and catheter 69.

The medical intervention called angioplasty is difficult to carry outbecause the image sub-sequences or the image sequence are formed ofbadly contrasted medical images, where the guide-wire, balloon, stentand vessel walls are hardly distinguishable on a noisy background andare moreover submitted to motions. According to the invention, theviewing system comprises means not only for acquiring and displaying asequence of images during the intervention, but for processing anddisplaying said images, which are greatly improved in real time duringthe intervention.

As illustrated by FIG. 1A, this system comprises initialization meansapplied to the original images for extracting and localizing the objectof interest, which is usually moving with respect to the referential ofthe image, but not necessarily, the background being moving both withrespect to said referential and with respect to the object. Theextraction and localization means may localize the object directly.However, as the objects are hardly radio-opaque, they are preferablylocalized indirectly. According to the invention, the objects arelocalized by first localizing related markers. The initialization meansthen comprise registration means for registering the moving object ofinterest with respect to the image referential. This system furthercomprises processing means including at least a means for carrying out atemporal integration technique performed on at least two images. Thistechnique is efficient to enhance the object of interest because saidobject has previously been registered with respect to the referential ofthe images. Since after registration of the object, the background stillmoves with respect to the referential of the images, the temporalintegration technique provides sharp detail enhancement of the object ofinterest, while the details of the background are blurred. In otherwords, with the technique of the invention, the integration stepintegrates object pixels that correspond to same object pixels insuccessive images, so that their intensities are increased, while saidintegration step integrates background pixels that do not correspond tothe same background pixels in the successive images, so that theirintensities are decreased.

Hence, the important means of the invention is in fact a motioncorrected temporal integration means, wherein the motion correction isapplied to the object of interest and not to the background, while thetemporal integration is applied both to the object of interest and tothe background. In an example, the temporal integration means maycomprise averaging means for averaging the pixel intensities, at eachpixel location in the referential, on two or more images. In anotherexample, the temporal integration means may comprise a recursive filter,which performs a weighted average of pixel intensity on succeedingimages.

The enhancement of the object may be compared to the one obtained byhaving applied to the object an increase of the dose of x-rays duringthe formation of the sequence of images, since the intensities of thepixels of the object are increased due to the integration over severalimages. However, according to the invention, for efficiency of thetemporal integration, this step is carried out on corresponding pixels,i.e. on a static object, which is obtained by the registration of theobject performed in the preliminary steps. Now, regarding thebackground, the result obtained by temporal integration is completelydifferent from the one obtained by increasing the dose of x-rays. Sinceaccording to the invention, after the registration step, the object isimmobile with respect to the referential of the image, while thebackground still moves with respect to the object, it results that, bytemporal integration, the background is blurred, smoothed and faded, thenoise is minimized, while the details of the object are enhanced.Instead, by increasing the dose of x-rays, the details of the backgroundwould be enhanced in the same way as those of the object, which is notdesirable. Increasing the dose of x-rays would also present theinconvenient to be dangerous for the patient and the clinician.

An advantageous integration means may comprise a determination of theresemblance of the object called object of interest detected in twosuccessive images. In fact, if two different objects were detected, andintegrated, their pixels would not correspond and the result of theintegration step would be a blurred object. The determination ofresemblance between an object of interest in a first image and thecandidate to be called same object of interest in a succeeding image isperformed using a criterion of similarity. This advantageous integrationmeans comprises means to modulate an object pixel intensity in thecurrent image in function of the result of the criterion. The system ofthe invention further comprises sharp detail enhancement means appliedto the image after the first temporal integration. Then, the system mayfurther comprise a second registering means that compensates for theremaining fine motion of the object with respect to the referential ofthe image and a second temporal integration phase to refine the objectenhancement. The temporal integration technique applied to registeredobjects presents several essential advantages over using an increase ofx-ray dose, without the inconvenient.

In the present example of application to cardiology, the user of theviewing system may be an actor of the medical intervention. In thiscase, he has the possibility to intervene during the image processingsteps, for example while not moving the intervention tool or tools.First of all, the user might choose a region of interest in the images.Besides, the user has at his disposal control means 58, shown in FIG. 5,to activate and control the image processing means. These control meanscomprise starting means and stopping means for the user to start theimage processing operation, to control the duration of the imageprocessing operation and to end the image processing operation. Inparticular, the user may choose that the final processed images arecompensated for the registration or not, depending on whether the motionof objects is of importance for the diagnosis or not.

Referring to FIG. 1A, the initialization means includes extracting means11 that solves the problems of accurately localizing the object ofinterest in the sequence. The object of interest are preferablylocalized indirectly by localizing first specific features such as theguide-wire tip 63 or the balloon-markers 61, 62 or 71, 72. The marker63, which is located at the extremity of the thin guide-wire 65, permitsof determining the position of the guide-wire 65 with respect to thestenosed zone 80 a of the artery 81; the balloon-markers 61, 62, whichare located on the monorail 60 at a given position with respect to theballoon 64, permit of determining the position of the first balloon withrespect to the stenosed zone before expanding the balloon in the lumenof the artery; the balloon-markers 71, 72, which are located on themonorail 70 at a given position with respect to the balloon 74 a, permitof determining the position of the second balloon, with the stent 75 awrapped around it, before stent expansion and permits of finallychecking the expanded stent 75 b.

These specific features called tips or markers are far better contrastedthan the stent or vessel walls. The extracting means 11 are appropriateto accurately extract said tips or markers from the original images 10.However, the clinician may choose to select the tips and markersmanually or to improve manually the detection of their coordinates.These tips and markers have a specific easily recognizable shape, andare made of a material highly contrasted in the images. Hence they areeasy to extract. It is to be noted that these specific features do notpertain to the badly contrasted stent or vessel walls, which are theobjects that are actually finally of interest for the practitioner. Theguide-wire tip 63 pertains neither to the artery walls 81 nor to thestent 75 a, since it pertains to the guide-wire 65. Also, theballoon-markers 61, 62 or 71, 72 pertain neither to the vessel walls 81nor to the stent 75 a since they pertain to the monorail 60 or 70. Thesystem processing means 11 permits of accurately deriving the locationof the balloons 64, 74 a, 74 b, since the balloon-markers have aspecific location with respect to the balloons. Also, the stents 75 a,75 b are accurately localized, since the stents have a specific locationwith respect to the balloon-markers though said stents are not attachedto said balloon-markers. Once the markers of an object of interest hasbeen extracted, the registering means 12 registers the object ofinterest with respect to the referential of the images 10, preferablybased on the marker location.

Referring to FIG. 3, for instance two markers A_(Ref), B_(Ref) have beendetected in an image of the sequence, called image of reference, whichmay be the image at starting time. The markers A_(Ref), B_(Ref) may beselected by automatic means. Then, the registering means 12 of thesystem, using the marker location information A_(Ref), B_(Ref) in thereference image and corresponding extracted markers A′_(t), B′_(t) in acurrent image of the sequence 10, are operated for automaticallyregistering the current image on the reference image. This operation isperformed by matching the markers of the current image to thecorresponding markers of the reference image, comprising possiblegeometrical operations including: A translation T to match a centroidC_(t) of the segment A′_(t)B′_(t) of the current image with a centroidC_(Ref) of the segment A_(Ref)B_(Ref) of the reference image; a rotationR to match the direction of the segment A′_(t)B′_(t) of the currentimage with the direction of the segment A_(Ref)B_(Ref) of the referenceimage, resulting in a segment A″_(t)B″_(t); and a dilation Δ formatching the length of the resulting segment A″_(t)B″_(t) with thelength of the segment A_(Ref)B_(Ref) of the reference image, resultingin the segment A_(t)B_(t). Such operations of translation T, rotation Rand dilation Δ are defined between the current image at a currentinstant t of the sequence and an image of reference, resulting in theregistration of the whole sequence. This operation of registration isnot necessarily performed on all the points of the images. Zones ofinterest comprising the markers may be delimited.

This operation of registration minimizes the effect of respectivemovements of the objects of interest, such as vessels, guide-wire,balloons and stent, with respect to a predetermined image referential.Preferably, two markers, or more, are used for better registration. Theregistration operation permits the user to easily perform a zooming Z onthe object of interest, without the object evading from the frame of theimage.

In the registered sequence 13, the pixels of the object of interest arenow approximately static in the succeeding images. So, according to theinvention, a registered object of interest is submitted to a firsttemporal integration means 14 over a first number of images, at leasttwo images or more than two images; this first integration phase isdenoted by TI₁. The first number of images for the first temporalintegration is chosen according to a compromise to avoid blurring theobject having residual motion and to cause the blurring of thebackground. As the background has not been registered with respect tothe referential of the image, the details of the background are stillmoving with respect to the object. By integrating the approximatelystatic pixels using the first temporal integration means, the intensityof each pixel is increased, while the details of the background areblurred. In an example, the registered images 13 are integrated byaveraging means applied to the intensity of the pixels on the firstnumber of images. By this operation, the details of objects, such asvessels, which are substantially in time concordance, are enhanced andthe noise is minimized, while the details of the background, which arenot in time concordance, are blurred. In another example, the temporalintegration means is a recursive filter for combining the currentoriginal image at an instant t, where the intensities are denoted byX(t), to the image processed at a previous instant (t−1), where theintensities are denoted by Y(t−1), using a weighting coefficient β,according to a formula giving the intensities of the integrated currentimage:Y(t)=Y(t−1)+β[X(t)−Y(t−1)]  [1]Using this last technique, the images are more and more improved as thesequence proceeds. This operation yields an intermediate sequence 15 ofregistered enhanced images with a blurred background, further used forsharp detail enhancement.

Creating a view in which the object of interest is registered andtemporally integrated is a way to improve the visibility and reduce thenoise. However, if the registration fails in one of the frames becauseof a wrong detection, the visibility of the object of interest in thetemporal integrated view may decrease dramatically. This problem mightarise anytime temporal integration is involved. Referring to FIG. 1B,according to the invention, the solution consists in checking theresemblance of the current not yet integrated (possibly registered)frame X(t) with the previously integrated view Y(t−1) in order todetermine resemblance information, which resemblance information is thenused to determine a modulation coefficient α. Said modulationcoefficient α is further used in order to modulate the importance of thecurrent frame in the registered view Y(t), during temporal integration.The resemblance information between X(t) and Y(t−1) is measured by asimilarity criterion 16, denoted by R. This similarity criterion R maybe a correlation or a normalized correlation. If the criterion R gives alow result, the weight of the current image X(t) in Y(t) will be low.

The temporal integration 14 may be recursive, hence the weight is α(t)that depends on time. In that case:Y(t)=α(t).Y(t−1)+(1−α(t)).X(t)  [2]with α(t)=f(R(t)).

The previously temporally processed sequence of images with blurredbackground 15 is submitted to the enhancing means 21, which may be aspatial filter such as an edge filter. This edge filter extracts thesharp details of the object of interest and yields images of edges 22.The user may choose to restore the motion of the objects beforedisplaying the sequence of images. In this case, the sharp detailenhancement means 21 yields the images of edges 22 to inverseregistration means denoted by registration means power minus one 31 a,which causes motion restitution. The images with restored motion arecombined by combination means 32 a to the input images 10 to yield afirst interesting image sequence 41 of original objects with enhancededges and with their original motion and original background, to bedisplayed to the user on the display means 54 of the viewing systemshown on FIG. 5. The images of edges 22, yielded by said sharp detailenhancement means 21, may alternately be entered together with theregistered images 13, yielded by the registration means 12, in acombination means 32 b for enhancing the edges of the objects in theregistered images 13. This combination means 32 b yields a secondinteresting image sequence 42 of registered objects with enhanced edgeson the original background, to be displayed on the display means 54.

The registered images 42 with enhanced sharp details, issued by thecombination means 32 b, are further submitted to a second registrationmeans to eliminate residual motion of the object, because in fact, afterthe first registration performed by means 12, the object of interest maystill be submitted to small residual motion with respect to the imagereferential, for the reason that the markers are the actually registeredfeatures and that said markers are not attached to the object ofinterest. Then, the images are submitted to a second temporalintegration means 33 a for causing background fading. The secondtemporal integration technique may be the same as the first one. Thesecond integration phase may be performed on a second number of images,preferably greater than or equal to the first number used in the firstintegration means 14, and is denoted by TI₂. The second temporalintegration phase TI2 has for advantage to provide a third interestingsequence of images 43 with motion registration, sharp featureenhancement of the objects of interest and background fading, to bedisplayed on the display means 54. The previously enhanced objects areagain enhanced while the moving details of the background are faded.

Now that the objects are registered in the images and that the detailsare enhanced, the user can easily zoom on details of an object with theadvantage that the object does not evade from the frame of the image.This zooming possibility is particularly important in the operation ofballoon and stent positioning.

It has been noted above that, thanks to the image processing means ofthe invention, it is no more necessary for the practitioner to introducea contrast agent in the balloon for inflating the balloon, since theballoon is better visualized together with the stent without contrastagent. This property is also particularly useful when it is necessary tovisualize a sequence of images of an intervention comprising theintroduction and positioning of two stents side by side in the sameartery. The first stent is clearly visualized after its deployment. Thenthe second stent is visualized and located by the detection of itsmarkers. These objects are further registered and enhanced, whichpermits the practitioner of visualizing the second balloon duringinflation and the stent during deployment, in dynamic instead of instatic as was the case when contrast agent was necessary to localize theballoon. Normally, the practitioner may position the two stents verynear from one another when necessary because their visualization isexcellent.

The user may choose to examine the sequence of images with the originalmovements of the objects. In this case, the second temporal integrationmeans 33 a yields the images 42 to inverse registration means 31 b,which causes motion restitution and yields a fourth interesting imagesequence 44 of objects with enhanced edges and with their originalmotion and faded background, to be displayed on the display means 54 ofthe viewing system shown on FIG. 5. Now, the user may choose to simplyobserve the registered object on a faded background. In that case, theimages yielded by the registration means 12, possibly zoomed, areprovided to the second temporal integration means 33 b, denoted TI2, andfurther issued to the display means 54. It is to be noted that thissimple operation is efficient enough because the residual motion of theobject of interest is generally very small and because the background isgenerally rapidly fading after integration over a small number ofimages. This provides a fifth interesting image sequence 45 ofregistered objects with faded background, to be displayed on the displaymeans 54 of the viewing system shown on FIG. 5.

A computer executable image processing method to be used in a system asabove described has steps of processing a sequence of digital imagesduring the medical intervention, comprising extracting at least a markerthat pertains neither to the tool nor to the body organ, determining themarker location information in the images of the sequence, deriving theobject location information from the marker location information, andprocessing the images to improve the visibility of the tool and/or ofthe organ. The method permits of displaying the images during themedical intervention for the user to position the tool in the organ at aspecific location using these enhanced images. In the application toangioplasty, the result of these image processing operations for examplepermits of checking the proper expansion of the lumen of the artery andpermits of checking the proper expansion of the stent.

FIG. 4A shows an original image of a medical sequence representing acatheter, a guide wire, a balloon with balloon-markers (as two smalldark points) and an artery on a background of other organs. Thevisualization of the objects of interest (balloon and artery) is verydifficult. Even the balloon-markers are hardly visible. The doted linerepresents the frame of the zoomed image of FIG. 4B. In FIG. 4B, theimage has been processed according to the invention: hence the objectsof interest are enhanced and the background is completely faded.

The imaging system means and imaging method of the present inventionpermit of improving the images of the sub-sequence that are acquired asdescribed above in step c), in reference to FIG. 2C, in such a way thatthe medical intervention steps may be simplified. In fact, for deployingthe balloon in step c), starting from the shape 74 a to yield the shape74 b, the practitioner must introduce an inflation product into theballoon. Without the viewing system of the invention, the practitionergenerally uses an inflation product that comprises a large amount of acontrast agent in order to be able to visualize the balloon. Thiscontrast agent has for an effect to render the balloon and stent as asole dark object in the images of the sub-sequence. When using such acontrast agent, the balloon and stent are not distinguishable from oneanother during the balloon inflation and stent deployment. Thepractitioner must wait until the removing of the darkened balloon for atlast having a view of the deployed stent alone, and it is only a staticview. Instead, the imaging system means and imaging method of thepresent invention permit of avoiding the use of contrast agent in theinflation product, or to use a substantially small amount of such acontrast agent in the product during the operation of balloon inflationand stent deployment. Since the balloon now remains transparent, saidimaging system means and imaging method of the present invention permitof dynamically following the inflation of the balloon and stentdeployment in all the images of the sequence. Said imaging system meansand imaging method of the present invention permit of dynamicallyvisualizing the balloon and the stent independently during theoperations of inflation of the balloon and stent deployment. Thisresults are due to the fact that the object of interest are registeredin the images, zoomed and enhanced in such an improved manner that it isno more necessary to use the contrast gent to permit the practitioner oflocalizing and visualizing them. Of course, these results are onlyobtained thanks to the sophisticated means of the invention.

FIG. 5 shows a diagram of a medical examination apparatus 50. Theapparatus has means 51 for acquiring digital image data of a sequence ofimages, and is coupled to a medical viewing system 53 as describedabove, for processing these data according to the processing methodcited above. The medical viewing system is generally used in theintervention room or near the intervention room for processing real timeimages. Should steps of the present method be applied on stored medicalimages, for example for estimating medical parameters, the system forprocessing the data of the stored images would be called medical viewingstation. The medical examination apparatus provides the image data byconnection 57 to the system 53. The system provides processed image datato display and/or storage means. The display means 54 may be a screen.The storage means may be a memory MEM of the system 53. Said storagemeans may be alternately external storage means. This image viewingsystem 53 may comprise a suitably programmed computer, or a specialpurpose processor having circuit means such as LUTs, Memories, Filters,Logic Operators, that are arranged to perform the functions of themethod steps according to the invention. The system 53 may also comprisea keyboard 55 and a mouse 56. Icones may be provided on the screen to beactivated by mouse-clicks, or special pushbuttons may be provided on thesystem, to constitute control means 58 for the user to start, to controlthe duration or to stop the processing means of the system at chosenphases.

1. A viewing system for enhancing objects of interest represented on amoving background in a sequence of noisy images and for displaying thesequence of enhanced images, including acquisition means for acquiringthe sequence of images and processing means for processing the imagescomprising extracting means for extracting features related to an objectof interest on a background in images of the sequence having an imagereferential, said processing means further comprising: a firstregistering means, yielding registered images, for registering thefeatures related to the object of interest with respect to the imagereferential, while not registering the background; a first temporalintegration means for integrating both the object of interest and thebackground over at least two registered images of the sequence; a secondregistering means and a second temporal integrating means forintegrating the registered object of interest with enhanced edges andthe moving background over at least two images of the sequence, yieldingimages of the registered object of interest with enhanced edges andfaded background to the display means and display means for displayingthe processed images of the enhanced registered object of interest onfaded background.
 2. The system of claim 1, having control means for auser to activate the processing means, control duration of theprocessing means, or stop the processing means at a selected stage inthe sequence of images.
 3. The system of one of claim 1, wherein theprocessing means further comprises: similarity detection means fordetermining resemblance information in one or more representations of aregistered object of interest in succeeding images; and weighing meansusing said resemblance information for modulating the intensities of thepixels of said object of interest over the images of the sequence,during temporal integration by the temporal integration means.
 4. Thesystem of one of claim 1, wherein the processing means furthercomprises: enhancement means for spatially enhancing sharp details inthe images issued from the temporal integration means (14), yieldingimages of edges of the object of interest; combination means forcombining the registered images yielded by the first and secondregistration means and the images of edges yielded by a filtering means,yielding images of the registered object of interest with enhanced edgesto the display means.
 5. The system of claim 4, further comprisinginverse registration means to restitute the motion of the object ofinterest, yielding to the display means images of the object of interestmoving with respect to the image referential.
 6. The system of claim 5,wherein the inverse registration means to restitute the motion of theobject of interest is applied to the images of the registered object ofinterest with enhanced edges and faded background yielded by the secondtemporal integration means, yielding to the display means images of theobject of interest having enhanced edges, moving with respect to theimage referential, and with faded background.
 7. The system of claim 5,wherein the inverse registration means is applied to the images ofenhanced edges yielded by the spatial filter, to restitute the originalmotion to said enhanced edges, the system further comprising:combination means for combining the original images and the images ofedges with original motion, yielding to the display means images of theoriginal object of interest with enhanced edges.
 8. The system of claim1, wherein the first registration means further comprises zooming meansfor zooming a registered object of interest.
 9. The viewing system ofclaim 1, for dynamically displaying a sequence of medical images of amedical intervention that comprises moving and/or positioning a toolcalled balloon, in an artery, said balloon and artery being consideredas objects of interest, and said balloon being carried by a supportcalled monorail, to which at least two localizing features calledballoon-markers are attached and located in correspondence with theextremities of the balloon, wherein: the extracting means extracts theballoon-markers considered as features related to the objects ofinterest, which balloon-markers pertain neither to the balloon nor tothe artery; the registering means registers the balloon-markers and therelated balloon and artery in the images; the processing means,comprising at least temporal integration means and sharp detailenhancement means, yield images of enhanced balloon and artery; and: thedisplay means dynamically displays the images during the medicalintervention for the user to visualized images of the balloon during itspositioning in the artery, at a specific location of a portion of theartery, with respect to the balloon-marker extracted location.
 10. Thesystem of claim 1, for dynamically displaying a sequence of images of anintervention, which comprises moving and/or positioning a tool calledstent wrapped around a balloon in an artery, said balloon, stent andartery being considered as objects of interest, which stent and balloonare carried by the monorail to which at least two localizing featurescalled balloon-markers are attached and located in correspondence withthe extremities of the balloon, wherein: the extracting means extractsthe balloon-markers considered as features related to the objects ofinterest, which balloon-markers pertain neither to the balloon nor tothe stent and nor to the artery; the registering means registers theballoon-markers and the related balloon, stent and artery in the images;the processing means, comprising at least temporal integration means andsharp detail enhancement means, yield images of enhanced balloon, stentand artery; and: the display means dynamically displays the imagesduring the medical intervention for the user to visualize images of theballoon during its positioning in the artery, at a specific location ofa portion of the artery, with respect to the balloon-marker extractedlocation; the display means dynamically displays the images during themedical intervention for the user to visualize images of the balloonwith the stent during their positioning in the artery, at a specificlocation of a portion of the artery, with respect to the balloon-markerextracted location, and for the user to further visualize images of thestent deployment during a stage of balloon inflation with an inflationproduct without or with substantially few contrast agent.
 11. The systemof claim 9, comprising: selecting means for selecting an image of thesequence called reference image, and at least a marker called referencemarker in the reference image related to an object of interest; andsystem wherein: the first registering means uses the marker locationinformation in the reference image and in a current image of thesequence, for registering the marker and the related object of interestof the current image by matching the marker of the current image to thereference marker of the reference image.
 12. A computer executable imageprocessing method, for enhancing objects of interest represented on amoving background in a sequence of noisy images, for displaying thesequence of enhanced images, for acquiring the sequence of images, forprocessing the images, and for extracting features related to an objectof interest on a background in images of the sequence having an imagereferential, the method comprising acts of: registering the featuresrelated to the object of interest with respect to the image referential,while not registering the background, yielding registered images;temporally integrating both the object of interest and the backgroundover at least two registered images of the sequence; registering andtemporally integrating the registered object of interest with enhancededges and the moving background over at least two images of thesequence, yielding processed images of the registered object of interestwith enhanced edges and faded background; and displaying the processedimages of the enhanced registered object of interest on fadedbackground.
 13. A computer readable medium having processor-executableinstructions thereon which, when executed by a processor, direct theprocessor to carry out an image processing method for enhancing objectsof interest represented on a moving background in a sequence of noisyimages, for displaying the sequence of enhanced images, for acquiringthe sequence of images, for processing the images, and for extractingfeatures related to an abject of interest on a background in images ofthe sequence having an image referential, the processor-executableinstructions comprising: a portion for registering the features relatedto the object of interest with respect to the image referential, whilenot registering the background, yielding registered images; a portionfor temporally integrating both the object of interest and thebackground over at least two registered images of the sequence; aportion for registering and temporally integrating the registered objectof interest with enhanced edges and the moving background over at leasttwo images of the sequence, yielding processed images of the registeredobject of interest with enhanced edges and faded background; and aportion for providing the processed images of the enhanced registeredobject of interest on faded background to a display device fordisplaying.
 14. A medical examination imaging apparatus having means foracquiring a sequence of medical images and having a viewing system forprocessing and for displaying said sequence of images according to claim1.